The research, led by Alberto Borges, an oceanographer and head of the CO2 Lab at the University of Liège, represents the largest investigation of its kind ever conducted. The team carried out 503 individual measurements spanning lakes that range from oligotrophic systems with very low algal biomass and strikingly clear waters to hypereutrophic lakes whose waters are rendered green by dense blooms of phytoplankton, the community of microscopic algae suspended in the water column. This extraordinary gradient of lake types allowed the researchers to test, at continental scale, what actually controls the fate of methane once it is produced in lake sediments and diffuses upward through the water.

To understand why this finding matters, it helps to consider the underlying chemistry and microbiology of methane in freshwater systems. Methane emissions from a lake, as Borges explains, are the result of a balance between two opposing processes. On the production side, methanogenesis occurs in the oxygen-free sediments at the bottom of the lake, where archaeal microorganisms decompose organic matter and release methane as a metabolic byproduct. On the loss side, microbial oxidation takes place in the water column, where a specialized group of bacteria known as methanotrophs consume methane as their preferred substrate, using it both as a source of energy and as the raw material for building their own biomass. The net emission that reaches the atmosphere is simply what remains after this microbial consumption has had its effect.

The central discovery of the new study is that methane oxidation increases sharply with the amount of microalgae present in the water. The surfaces of these algae are colonized by communities of bacteria, and among them are methanotrophs that exist in a mutually beneficial relationship with their algal hosts. The methanotrophs supply the algae with carbon dioxide, which the algae use for photosynthesis, while the algae in turn produce the oxygen that the bacteria require to oxidize methane. This tight metabolic coupling means that the more abundant the microalgae become, the more abundant the methanotrophic bacteria become as well, and the more intense the oxidation of methane turns out to be. In the most productive lakes studied, oxidation rates reached levels tens of thousands of times higher than those measured in the poorest lakes.

The scale of this consumption is far from trivial. According to the study, oxidation is the main fate of methane dissolved in the surface waters of the lakes examined, eliminating more than 70 percent of it. That is substantially more methane than ultimately escapes into the atmosphere, which means that without this bacterial activity, lake emissions would be considerably higher than current estimates suggest. The finding reframes the way scientists think about the greenhouse gas budget of inland waters, because a process that was often treated as a secondary detail in methane cycling turns out to be the dominant control on how much methane actually reaches the air.

The study also uncovered a second, geographically distinct source of intense methane oxidation. Lakes bordered by the flooded forests of the Congo Basin were characterized by particularly high levels of oxidation, fueled by an influx of bacteria originating from the submerged forest soils. This suggests that the connection between terrestrial ecosystems and lake methane dynamics extends beyond the simple delivery of organic carbon. Flooded forests appear to seed adjacent waters with methanotrophic communities, adding another layer of biological control to the methane budget of these tropical systems and highlighting the importance of riparian and wetland vegetation in regulating greenhouse gas fluxes.

What makes the result especially consequential is how it interacts with the ongoing global problem of eutrophication, the enrichment of waters with nutrients that drives excessive algal growth. Earlier work by the same team had shown that as phytoplankton biomass increases, methane production in the sediments increases as well, because algal detritus sinking to the lake bottom serves as a rich feedstock for the methane-producing microorganisms living there. On its own, that relationship painted a worrying picture: the greener and more polluted a lake becomes, the more methane it should emit. The new study demonstrates that the reality is more nuanced, because two opposing effects occur simultaneously in eutrophic waters.

As pollution drives phytoplankton to proliferate, methane production in the sediments rises, but the methanotrophic bacteria attached to the algae multiply in parallel and consume an increasing share of that methane. Crucially, in the lakes studied, the increase in oxidation can outweigh the increase in production. In the absence of these algae-associated bacteria, methane emissions into the atmosphere would be much higher than what is actually observed. The bacteria therefore act, in Borges’s words, as natural and welcome filters that partially mitigate the effect of lake pollution on global warming. It is an important piece of the puzzle that was missing, and one that will allow researchers to better predict the future trajectory of methane emissions from lakes as eutrophication continues to spread across the tropics and beyond.

The implications extend well beyond African lakes. Tropical and subtropical freshwaters are among the most productive ecosystems on Earth, and many are experiencing accelerating nutrient loading from agriculture, urbanization, and wastewater discharge. If the coupling between phytoplankton and methanotrophs documented here proves to be a general feature of productive lakes, then global methane budgets for inland waters may need to be revised downward, and the models used to project future emissions will need to incorporate algal-bacterial symbiosis as a first-order control rather than a footnote. Conversely, any environmental change that disrupts this symbiosis, such as shifts in nutrient regimes, light availability, or water chemistry, could tip the balance back toward greater emissions.

For now, the study stands as a vivid reminder that the climate system is shaped not only by vast physical processes but also by intimate partnerships between microscopic organisms. On the surface of a single algal cell drifting in a green African lake, a bacterium consumes methane and exhales carbon dioxide that the alga immediately recycles into oxygen and organic matter. Multiplied across hundreds of lakes and billions of microbial encounters, this quiet exchange removes the majority of the methane that would otherwise warm the planet. Understanding and protecting such natural filters may prove to be an essential part of anticipating how freshwater ecosystems will respond to a changing, increasingly nutrient-rich world.

Subject of Research: Methane oxidation by algae-associated methanotrophic bacteria in African lakes

Article Title: In African lakes, microbes living on algae reduce a powerful greenhouse gas

Article References: In African lakes, microbes living on algae reduce a powerful greenhouse gas. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: methane, methanotrophs, microalgae, African lakes, eutrophication, greenhouse gases, phytoplankton, Nature Communications, University of Liège, Congo Basin, biogeochemistry, freshwater emissions

Researchers from Southern Cross University, together with a colleague from NASA’s Goddard Space Flight Center and the University of Maryland, carried out four field campaigns in a subtropical Australian rainforest, measuring methane fluxes from both tree stems and forest soils. Their study plots were deliberately positioned along a moisture gradient: a valley floor plot where water lingers, a lower slope plot, and an upper slope plot where the ground drains freely. This design allowed the team to isolate one of the most important controls on methane cycling in any landscape, the availability of oxygen in the soil.

The underlying science is a contest between two microbial communities. In aerated soils, methanotrophic bacteria consume methane from the atmosphere, oxidizing it for energy and acting as a biological filter that removes this potent greenhouse gas before it can accumulate. But when soils become saturated, oxygen disappears, and a different group of microbes, the methanogenic archaea, takes over, producing methane as a byproduct of anaerobic decomposition. Whether a forest soil is a net sink or a net source of methane depends on which of these processes dominates, and that, in turn, depends heavily on soil moisture.

The study’s findings show that this dominance can flip with the seasons. On the valley floor, the researchers documented a remarkable transition: at the end of the dry season, the soil absorbed methane at a rate of about 151 micromoles per square meter per day, acting as a modest sink. But by the end of the wet season, the same soil had transformed into a powerful methane source, emitting around 830 micromoles per square meter per day. That is a swing of nearly a thousand micromoles per square meter per day driven almost entirely by changing water conditions, a magnitude of seasonal variability that underscores how misleading single-visit field measurements can be when estimating a landscape’s true greenhouse gas budget.

The sloped plots told a steadier story. On the lower slope, soils absorbed methane at an average rate of 135 micromoles per square meter per day, while the upper slope soils absorbed slightly more, at 156 micromoles per square meter per day. Crucially, these drier positions maintained their methane-consuming function throughout the year, remaining reliable sinks regardless of season. Because upland forests cover vast areas of the planet, this finding reinforces the significance of well-drained forest soils as one of the biological world’s most important natural defenses against methane accumulation in the atmosphere.

But the soil was only half the investigation. In recent years, scientists have increasingly recognized that trees themselves can act as conduits for methane, drawing dissolved gas up from waterlogged soils through their vascular systems and venting it from their stems, or hosting methane-producing microbes within their own tissues. Whether these stem emissions are significant enough to undermine the methane-removal service provided by upland forest soils has remained one of the field’s most pressing open questions.

Across most of the study site, the answer was reassuring. In the sloped plots, tree stems emitted negligible amounts of methane, and their tiny emissions offset less than one percent of the methane being consumed by the surrounding soils. In other words, the upland rainforest kept its carbon credentials intact: soils continued to scrub methane from the atmosphere, and the trees did little to undo that work. This is an important benchmark for global models, which must decide how much attention to give tree stem fluxes in dry upland settings, and it suggests that in such environments the soil sink comfortably dominates.

The valley floor was another matter. At the end of the wet season, when the saturated soil was already releasing methane in earnest, the trees added substantially to the problem. Stem emissions there contributed an extra 27 percent on top of the soil source, effectively amplifying an already large methane flux. The mechanism is intuitive: when soil air spaces fill with water, methane produced below ground can escape upward more readily through the aerenchyma and transport tissues of trees than through the waterlogged soil itself, making trees the path of least resistance for gas trying to reach the atmosphere.

Among the more striking discoveries were two individual trees that the researchers describe as high emitters. These outliers vented methane at rates two hundred and three hundred times higher than neighboring trees of comparable size on the same plots. Such extreme individual variability has been noted in other forest systems, but documenting it in a subtropical rainforest highlights a persistent challenge for field scientists and modelers alike: a small number of anomalous trees can disproportionately influence plot-level emissions estimates, particularly if they cluster in wetter microsites. Understanding what makes certain trees such efficient methane conduits, whether it is their rooting depth, stem anatomy, associated microbial communities, or proximity to methane-rich soil layers, is now a priority for follow-up work.

Statistically, the study found that both tree stem and soil methane fluxes correlated significantly and positively with soil moisture, confirming the moisture gradient as the master variable governing methane exchange in this ecosystem. This relationship has implications well beyond one Australian forest. As climate change alters rainfall patterns, intensifying both droughts and deluges in many subtropical regions, the moisture status of forest soils will shift accordingly, and with it the delicate balance between methane consumption and production. Periods of unusual wetness could temporarily convert upland landscapes that normally function as methane sinks into net emitters, while prolonged drying could expand the spatial footprint of the sink.

The research also carries lessons for how greenhouse gas inventories should be constructed. Because the valley floor transitioned between sink and source within a single year, any sampling campaign that visits a site only once, in either the wet or the dry season, risks capturing a snapshot that badly misrepresents the annual picture. The authors emphasize the high spatial and temporal heterogeneity of tree and soil methane fluxes in upland forests, a heterogeneity that demands repeated, seasonally distributed measurements across topographic gradients if regional and global methane budgets are to be trustworthy.

For the broader public, the takeaway is both sobering and hopeful. Sobering, because even pristine rainforests are not immune to climate feedbacks: wetter soils and methane-venting trees can tip natural ecosystems into contributing to the very problem they help mitigate. Hopeful, because the study confirms that the drier, extensive portions of subtropical rainforest landscapes remain steadfast methane sinks year-round, quietly removing a powerful greenhouse gas from the air at rates that matter globally. Protecting these forests, and the complex moisture gradients within them, preserves not only biodiversity and carbon storage but also this often-overlooked methane-scrubbing service.

The work, conducted with support from the Australian Research Council, the Hermon Slade Foundation, and other funders, adds a valuable subtropical data point to a global dataset still dominated by temperate and boreal measurements. As the search intensifies for natural systems that help regulate atmospheric methane, this study makes clear that the answer lies in the ground as much as in the canopy, and that the ground’s verdict changes with the weather.

Subject of Research: Seasonal methane fluxes from tree stems and soils along a soil moisture gradient in a subtropical Australian rainforest

Article Title: Seasonal changes in tree stem and soil methane fluxes along a soil moisture gradient in a subtropical Australian rainforest

Article References: Dittmann, J., Maher, D. T., Johnston, S. G., Das, A., Padilla-Montalvo, J. A., Stovall, A. E. L., & Jeffrey, L. C. (2026). Seasonal changes in tree stem and soil methane fluxes along a soil moisture gradient in a subtropical Australian rainforest. Biogeochemistry. https://doi.org/10.1007/s10533-026-01371-7

Image Credits: AI Generated

DOI: 10.1007/s10533-026-01371-7

Keywords: methane flux, rainforest, soil moisture, tree stems, greenhouse gases, methanotrophs, methanogenesis, soil sink, biogeochemistry, subtropical forest, seasonal variation, climate change